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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="fusion.functional"></a><a class="link" href="functional.html" title="Functional">Functional</a>
</h2></div></div></div>
<div class="toc"><dl class="toc">
<dt><span class="section"><a href="functional/concepts.html">Concepts</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/concepts/callable.html">Callable Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/reg_callable.html">Regular Callable
        Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/def_callable.html">Deferred Callable
        Object</a></span></dt>
<dt><span class="section"><a href="functional/concepts/poly.html">Polymorphic Function
        Object</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/invocation.html">Invocation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/invocation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/invocation/metafunctions.html">Metafunctions</a></span></dt>
<dt><span class="section"><a href="functional/invocation/limits.html">Limits</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/adapters.html">Adapters</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/adapters/fused.html">fused</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_procedure.html">fused_procedure</a></span></dt>
<dt><span class="section"><a href="functional/adapters/fused_function_object.html">fused_function_object</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused.html">unfused</a></span></dt>
<dt><span class="section"><a href="functional/adapters/unfused_typed.html">unfused_typed</a></span></dt>
<dt><span class="section"><a href="functional/adapters/limits.html">Limits</a></span></dt>
</dl></dd>
<dt><span class="section"><a href="functional/generation.html">Generation</a></span></dt>
<dd><dl>
<dt><span class="section"><a href="functional/generation/functions.html">Functions</a></span></dt>
<dt><span class="section"><a href="functional/generation/metafunctions.html">Metafunctions</a></span></dt>
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<p>
      Components to call functions and function objects and to make Fusion code callable
      through a function object interface.
    </p>
<h4>
<a name="fusion.functional.h0"></a>
      <span class="phrase"><a name="fusion.functional.header"></a></span><a class="link" href="functional.html#fusion.functional.header">Header</a>
    </h4>
<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">fusion</span><span class="special">/</span><span class="identifier">functional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
</pre>
<h4>
<a name="fusion.functional.h1"></a>
      <span class="phrase"><a name="fusion.functional.fused_and_unfused_forms"></a></span><a class="link" href="functional.html#fusion.functional.fused_and_unfused_forms">Fused
      and unfused forms</a>
    </h4>
<p>
      What is a function call?
    </p>
<pre class="programlisting"><span class="identifier">f</span> <span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">,</span><span class="identifier">c</span><span class="special">)</span>
</pre>
<p>
      It is a name and a tuple written next to each other, left-to-right.
    </p>
<p>
      Although the C++ syntax does not allow to replace <code class="literal">(a,b,c)</code>
      with some Fusion <a class="link" href="sequence.html" title="Sequence">Sequence</a>, introducing
      yet another function provides a solution:
    </p>
<pre class="programlisting"><span class="identifier">invoke</span><span class="special">(</span><span class="identifier">f</span><span class="special">,</span><span class="identifier">my_sequence</span><span class="special">)</span>
</pre>
<p>
      Alternatively it is possible to apply a simple transformation to <code class="literal">f</code>
      in order to achieve the same effect:
    </p>
<pre class="programlisting"><span class="identifier">f</span> <span class="identifier">tuple</span> <span class="special">&lt;=&gt;</span> f' <span class="special">(</span><span class="identifier">tuple</span><span class="special">)</span>
</pre>
<p>
      Now, <code class="literal">f'</code> is an unary function that takes the arguments to
      <code class="computeroutput"><span class="identifier">f</span></code> as a tuple; <code class="literal">f'</code>
      is the <span class="emphasis"><em>fused</em></span> form of <code class="computeroutput"><span class="identifier">f</span></code>.
      Reading the above equivalence right-to-left to get the inverse transformation,
      <code class="computeroutput"><span class="identifier">f</span></code> is the <span class="emphasis"><em>unfused</em></span>
      form of <code class="literal">f'</code>.
    </p>
<h4>
<a name="fusion.functional.h2"></a>
      <span class="phrase"><a name="fusion.functional.calling_functions_and_function_objects"></a></span><a class="link" href="functional.html#fusion.functional.calling_functions_and_function_objects">Calling
      functions and function objects</a>
    </h4>
<p>
      Having generic C++ code call back arbitrary functions provided by the client
      used to be a heavily repetitive task, as different functions can differ in
      arity, invocation syntax and other properties that might be part of the type.
      Transporting arguments as Fusion sequences and factoring out the invocation
      makes Fusion algorithms applicable to function arguments and also reduces the
      problem to one invocation syntax and a fixed arity (instead of an arbitrary
      number of arbitrary arguments times several syntactic variants times additional
      properties).
    </p>
<p>
      Transforming an unfused function into its fused counterpart allows n-ary calls
      from an algorithm that invokes an unary <a class="link" href="functional/concepts/poly.html" title="Polymorphic Function Object">Polymorphic
      Function Object</a> with <a class="link" href="sequence.html" title="Sequence">Sequence</a>
      arguments.
    </p>
<p>
      The library provides several function templates to invoke different kinds of
      functions and adapters to transform them into fused form, respectively. Every
      variant has a corresponding generator function template that returns an adapter
      instance for the given argument.
    </p>
<p>
      Constructors can be called applying <a href="http://www.boost.org/libs/functional/factory" target="_top">Boost.Functional/Factory
      Library</a>.
    </p>
<h4>
<a name="fusion.functional.h3"></a>
      <span class="phrase"><a name="fusion.functional.making_fusion_code_callable_through_a_function_object_interface"></a></span><a class="link" href="functional.html#fusion.functional.making_fusion_code_callable_through_a_function_object_interface">Making
      Fusion code callable through a function object interface</a>
    </h4>
<p>
      Transforming a fused function into its unfused counterpart allows to create
      function objects to accept arbitrary calls. In other words, an unary function
      object can be implemented instead of (maybe heavily overloaded) function templates
      or function call operators.
    </p>
<p>
      The library provides both a strictly typed and a generic variant for this transformation.
      The latter should be used in combination with <a href="http://www.boost.org/libs/functional/forward" target="_top">Boost.Functional/Forward
      Library</a> to attack <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2002/n1385.htm" target="_top">The
      Forwarding Problem</a>.
    </p>
<p>
      Both variants have a corresponding generator function template that returns
      an adapter instance for the given argument.
    </p>
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      Dan Marsden, Tobias Schwinger<p>
        Distributed under the Boost Software License, Version 1.0. (See accompanying
        file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
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